An object of the present invention is a method for the testing of electronic components. It can be used more particularly in the testing of semiconductor electronic components, especially components such as integrated circuits. In the prior art, there is a known method for the testing of electronic components that reduces the unit testing time of each component. The value of the invention lies in the fact that it proposes a test method that first of all reduces the unit testing time and, secondly, optimizes the output efficiency of the goods tested.
The invention is an improvement of the international patent No. WO 97/45748, published on Dec. 4, 1997. The subject matter of this international patent is incorporated herein by reference. An electronic component generally comprises several functions. It is therefore subjected to a series of tests to test each one of its functions. The test method according to the document WO 97/45748 can be applied to each of the tests of a series such as this. A test generally comprises several successive elementary steps. Thus a method for the testing of an electronic component comprises the following elementary steps:
at an initial date Di, terminals of the component, considered to be input terminals with respect to the test, are subjected to an electric potential Vi,
there is a wait, during a period of time, for a response to appear and for this response to get stabilized at the terminals of this component, considered as output terminals with respect to this test,
at the end of this period of time, at a measurement date DM, this response is measured. In one example, a value Vs of a potential at these output terminals is measured.
During the test, the component has thus been subjected to a signal, and the response of the component to this signal has been measured at the end of a certain period of time. Then, to find out if the component has given an acceptable result or not for this test,
the measured response is compared with fixed criteria of acceptance. That is, in this example, the value of the potential Vs is compared with lower and/or higher limits of acceptance.
Since the electronic component has a known structure, it is possible to theoretically determine the period of time at the end of which an expected response can be observed at the output of the component following the application of a potential Vi at the input terminals of this component. With this theoretical time being known, for example as calculated by the designer of the electronic component, a nominal measurement date Do is determined for this test. The nominal measurement date Do is a date after the initial date Di. Moreover, the nominal measurement date is such that the duration that elapses between the initial date Di and this nominal date Do is greater than the duration of the theoretical time. Indeed, to define this nominal date Do a safety margin is chosen.
Then, the nominal date Do is used as a measurement date DM for the components to be tested. This choice, which gives preference to the guarantee of a result that complies with the test, leads to an increase in the total time of the performance of the test. Since this is true for all the tests of the series of tests applied to the component, the total testing time for such a component is thus very considerably increased.
The international application WO 97/45748 envisages a test method to decrease the period of time between the initial date Di and the measurement date Dm. Indeed, since the test method is designed to be applied consecutively to thousands, or even more, of electronic components that are themselves made in batches, the test method applied to the set of these components comprises, according to this document:
a first xe2x80x9clearning phasexe2x80x9d and
a second xe2x80x9capplication phasexe2x80x9d.
In the learning phase, a population of acceptable components of the batch to be tested is considered. The acceptable components are those that have given a good result in the test performed at a measurement date Dm equal to the nominal measurement date Do. This population is a xe2x80x9cpopulation for learningxe2x80x9d hereinafter called a xe2x80x9clearning populationxe2x80x9d. In one example, this learning population may comprise a single electronic component.
Then, using the results obtained on this learning population, it is sought to define a measurement date that is the earliest possible measurement date. For this purpose, the test already performed on this learning population is reiterated, by again applying a signal to the input terminals and reading the value of the potential Vs at the output terminals on an intermediate measurement date Dmi, preferably prior to the nominal measurement date Do. If the learning population comprises a single component, then the same test is reiterated by using the same measurement date Dmi or Do to obtain several results for each of the dates tested.
Thus, a dichotomized or step-by-step procedure is carried out to test the measurement dates prior to the nominal date. To choose a measurement date from among these intermediate measurement dates Dmi tested, a comparison is made between:
a statistical image of the results of this learning population, obtained with an intermediate measurement date Dmi, and
a statistical image of the results of this same learning population, obtained on the nominal measurement date Do.
Indeed, for each intermediate measurement date Dmi tested, a statistical image of the results obtained is determined. This statistical image especially comprises the calculation of the mean M, and of the standard deviation S. Furthermore, to compare two statistical images with each other, a criterion of statistical appreciation is used. This criterion requires knowledge of the mean values and standard deviation values of the images to be compared. This a criterion of appreciation D referenced Cpi is defined for each statistical image obtained for a measurement date Dmi. In one example, this criterion of appreciation CPi is equal to a ratio between a difference in limit and the standard deviation. The difference in limits can be given by a manufacturer""s tolerance, for example To. Then CPi is equal to To divided by S.
To compare the statistical images with each other, their respective criteria of appreciation Cpi are compared. The earliest possible intermediate measurement date Dmi is chosen as the measurement date. This measurement date is furthermore such that the criterion of appreciation CPi is in a certain proportion of the criterion of appreciation CPo, where CPo is the criterion of appreciation characterizing the statistical image of the values measured at the nominal date Do.
The set of the statistical images determined for each of the intermediate measurement dates gives a representation of the evolution of the values measured at the output terminals after a signal VI has been imposed at the input terminals of this component.
In a first example, if for all the intermediate measurement dates Dmi tested, a wide range of values of the potential measured at the output is observed, without any predominance of any value, then it means that that the behavior of the electronic component under this test with these measurement dates is not reliable. Indeed, until the nominal measurement date Do, the potentials are fluctuating and are never correctly stabilized. In this case, it is impossible to choose a measurement date lower than the nominal measurement date.
In a second example, which is also unfavorable, even at the nominal measurement date Do, a curve is observed representing the values of non-stabilized potential measured at output. Then it is necessary to choose a measurement date which is higher than this nominal date.
In a third example, the representation of the evolution of the values measured at the exit of the electronic component is a curve plotted with a thin line. It is possible then to consider intermediate measurement dates that are correlated with the nominal measurement date. However, even in this example, it is possible to define a minimum measurement date, below which the statistical images of the results obtained with measurement dates lower than this minimum date are not consistent. For example, the result observed with the intermediate measurement date must remain within limits of acceptance imposed on the results obtained with the nominal measurement date.
The test method provides for the choice of an intermediate measurement date that is the earliest possible date but stipulates that this intermediate measurement date will, however, be higher than the minimum date.
Then this intermediate measurement date selected during the learning phase is applied as a measurement date DM for all the other electronic components to be tested. This intermediate measurement date is thus applied continuously during the application phase.
The approach proposed in the international application WO 97/45748 has several problems. A first problem of this method is the fact that it is necessary to carry out a learning phase prior to the testing of a batch of components. However this learning phase is lengthy, and entails loss of time. Moreover, the intermediate measurement date determined during this learning phase may be the cause of a higher rate of rejection of the electronic components tested during the application phase.
Given the duration of the learning phase, it cannot be done too frequently. The method therefore leads to the application of a measurement date not suited to a part of the batch to be tested. It is not possible, with the learning phase, to give the optimum intermediate measurement date for reducing the test time and also the optimum date for the profitability of the output tested. Indeed, if the learning phase has led to the choice of an excessively early intermediate measurement date, then many electronic components will fail the test carried out at this measurement date during the application phase. These components then will be wrongly removed from the standard output, and the ultimate profitability of the goods tested will be lower than the profitability that would have resulted from the performance of a test with a later measurement date.
It is an object of the invention to overcome the problems referred to by proposing a test method comprising a single learning phase whose teaching can be re-used during the test method application phase. In addition, the test method according to the invention proposes phases of adjustment of the measurement date during the application phase. Thus, regularly, for example at the end of a given number of parts tested, the measurement date is adjusted so that it is always optimized with respect to the duration of the testing of the production in progress, and optimized with respect to the profitability of this tested production. Indeed, since the characteristics of the production to be tested may be variable in time, the same measurement date cannot be applied continuously. It is necessary to adapt the measurement date to the specific characteristics of the production to be tested. Indeed, the characteristics of the output to be tested may be different in the course of time. And yet, it is not necessary to set aside these parts of the production from the population of acceptable components.
Furthermore, the invention proposes a test method in which the measurement date to be applied to a batch of components is determined by taking account of the intrinsic characteristics of the components to be tested. For this purpose, to determine the earliest possible measurement date, a population totalized by means of a criterion is considered. The totalized population comprises one or more components.
In a first example, a statistical image of this totalized population comprises results of this component or components obtained with distinct measurement dates. The operation of considering the population totalized according to this first example can be used as much during a learning phase as during an adjustment phase. In particular,
the components of the population xe2x80x9ctotalizedxe2x80x9d on the nominal measurement date are tested,
a nominal statistical image is determined,
the same components are tested on intermediate measurement dates,
a statistical image is considered of the totalized population comprising all the results obtained with the nominal measurement date and those obtained with an intermediate measurement date,
the statistical image of the totalized population is compared with the nominal statistical image by means of a criterion to determine if the intermediate measurement date incorporated into the totalized population can be chosen as the measurement date for the application phase.
In an alternative embodiment, a statistical image of this totalized population comprises results of components coming from different sources, but tested with same measurement dates. Then, this totalized population comprises, firstly, the acceptable components analyzed during the learning phase, and secondly the acceptable components of the adjustment phase. The components of the adjustment phase are acceptable components coming from the output tested during the application phase.
During this adjustment phase, a population of acceptable components is considered. For each adjustment phase, a totalized population is considered.
For each of the components of the learning phase, the measured values obtained at the various measurement dates are known. On the other hand, for the acceptable components considered during the adjustment phase, initially, only the value measured at the nominal measurement date is known. Only the acceptable components for a nominal measurement date can be included in the population of the adjustment phase. For these components of the adjustment phase, it is sought to establish the value measured at intermediate measurement dates earlier than the nominal measurement date. For each component contained in the population of the adjustment phase, the following step is carried out individually:
the value of the potential measured with different intermediate measurement dates is determined,
for each intermediate measurement date tested, the result of the component considered is included in the distribution of the results of the learning population, obtained for this intermediate measurement date,
a statistical image of this totalized population of values obtained on an identical measurement date is considered,
this statistical image of the totalized population is compared, by means of a criterion, with a statistical image of the learning population for values obtained on this same intermediate measurement date,
an adjusted intermediate measurement date is chosen such that this adjusted measurement date is higher than or equal to the earliest measurement date given for learning population, and such that a criterion of appreciation of the statistical image obtained for the totalized population is acceptable in comparison with a criterion of appreciation of the statistical image of the learning population obtained for this same adjusted measurement date.
An object of the invention is a method for the testing of electronic components in which
terminals of a component are subjected, at an initial date, to an electric potential,
a value of potential set up at terminals of this component is measured at a measurement date, and
this measured value of potential is compared with limits of acceptance, in order to accept or reject the component as a function of this comparison,
the measurement date is determined, during a learning phase preliminary to an application phase, by means of a criterion applied to a population of accepted components, in considering a statistical image of this population of accepted components,
the earliest possible date is chosen as a measurement date,
wherein:
the measurement date determined is adjusted in the course of at least one adjustment phase during the application phase.
An object of the invention is a also method for the testing of electronic components in which
terminals of a component are subjected, at an initial date, to an electric potential,
a value of potential set up at terminals of this component is measured at a measurement date, and
this measured value of potential is compared with limits of acceptance, in order to accept or reject the component as a function of this comparison,
the measurement date is determined by means of a criterion applied to a population of accepted components, in considering a statistical image of this population of accepted components,
the earliest possible date is chosen as a measurement date,
wherein
the population of accepted components considered is a totalized population comprising a total of a reference population and a population of acceptable components taken out of an application phase.